1. Field of the Invention
The present invention relates to a method of and an apparatus for converting input image data into output image data with conversion data established according to desired image processing conditions.
2. Description of the Related Art
In DTP (desktop printing), printing, and platemaking industries, there has widely been used a color image input and output system for obtaining input image data by reading a color subject with a scanner, effecting desired image processing on the input image data to generate output image data, and outputting a color image based on the output image data from an image output device such as a color printer, a CRT (cathode-ray tube), or the like.
The color image input and output system usually has color conversion function established with image processing conditions used as parameters. By establishing image processing conditions depending on an image, color conversion functions are defined to generate conversion data, and the input image data is subjected to desired image processing using the conversion data. The image processing conditions may include the type of subject image, density settings for highlights and shadows with respect to the input image data, and color correcting coefficients for color correction.
When an image is outputted on the basis of image data processed using conversion data thus established, if color conversion functions are established inappropriately, the output image may contain unnatural regions such as tone jumps. Specifically, color conversion functions described parametrically may not necessarily be established in a manner to be able to convert all image data highly accurately. For example, since conversion data established as a lookup table based on color conversion functions convert input image data into discrete output image data, an image with smaller density variations may suffer tone jumps due to large gradation changes.
It is a general object of the present invention to provide a method of and an apparatus for processing image data so as to be able to generate such conversion data which will not lower the gradation quality of an output image.
A major object of the present invention is to provide a method of and an apparatus for processing image data so as to be able to reduce tone jumps in images with smaller density changes and to maintain desired gradation reproducibility with respect to images with larger density changes.
Another object of the present invention is to provide a method of and an apparatus for processing image data so as to be able to smooth densities that are selected as desired.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.